cayocosta
Well-known member
Biasing a 12AX7 concertina phase splitter using a voltage divider from 243V B+. The plate and cathode resistors are both 56k.
Looking for -1.5V grid bias.
Here's what I tried:
2.2M/1M Divider:
Plate:169.9
Grid:71.0
Cathode:73.6
Bias:-2.6V
2M/1M Divider:
Plate: 168.7
Grid:74.6
Cathode: 76.5
Bias:-1.9V
1.8M/1M Divider:
Plate:167.0
Grid:76.7
Cathode:78.3
Bias:-1.6V
The 1.8M/1M divider did the trick - but none of the dividers gave me the voltage I expected to see:
1M / 2.2M+1M = .31 * 243V = 76V
1M / 2.0M+1M = .33 * 243V = 81V
1M / 1.8M+1M = .357 * 243V = 87V
Can someone help me understand what's going on?
Looking for -1.5V grid bias.
Here's what I tried:
2.2M/1M Divider:
Plate:169.9
Grid:71.0
Cathode:73.6
Bias:-2.6V
2M/1M Divider:
Plate: 168.7
Grid:74.6
Cathode: 76.5
Bias:-1.9V
1.8M/1M Divider:
Plate:167.0
Grid:76.7
Cathode:78.3
Bias:-1.6V
The 1.8M/1M divider did the trick - but none of the dividers gave me the voltage I expected to see:
1M / 2.2M+1M = .31 * 243V = 76V
1M / 2.0M+1M = .33 * 243V = 81V
1M / 1.8M+1M = .357 * 243V = 87V
Can someone help me understand what's going on?